I. Field of the Invention
The present invention relates generally to improvements in the performance of solid composite propellant compositions including those useful for a variety of rocket motors containing one or more plasticizers and binders, a fuel, and one or more oxidizers. More particularly, the invention is directed to improvements modifying the oxidizer fraction of the composition which significantly enhances the performance of rocket motors using the propellant. The invention is particularly applicable to propellent compositions of a class using metal fuel and containing relatively large amounts of ammonium perchlorate or ammonium nitrate in the oxidizer fraction. A significant amount of the ammonium compounds are removed and replaced by including a relatively large amount of bismuth oxide (Bi.sub.2 O.sub.3) as an oxidant in the oxidizer fraction.
II. Related Art
Solid rocket motor propellants have become accepted and widely used for the most part because they advantageously are relatively easy to manufacture and exhibit excellent performance characteristics. In addition, rocket motors utilizing solid fuel are generally a great deal less complex than those employing liquid fuels. The solid propellant is normally in the form of a propellant grain placed within the interior of the rocket motor and burned to produce quantities of hot gases which, in turn, exit through the throat and nozzle of the rocket motor at high velocity to provide thrust which propels the rocket in the opposite direction. An important consideration with regard to solid fuels is the amount of thrust available for a given volume of the propellant grain. Of course, the thrust is related to the mass and velocity of the material exiting the rocket motor. Increases in this factor, i.e., mass and/or velocity, of course, are desirable in order to increase total efficiency of the rocket motor itself. Thus, achieving an increase in the total thrust of a rocket motor, without the necessity of increasing its size, an impulse-and-density product gain, is one important sought-after fuel improvement goal.
It is known to use bismuth oxide (Bi.sub.2 O.sub.3) as a constituent in certain solid propellant compositions. Thus, as disclosed by Neidert et al. in U.S. Pat. No. 5,372,070, Bi.sub.2 O.sub.3 has been used as a relatively non-toxic, non-hazardous burn rate modifier to replace lead or other toxic materials in nitrate ester/ammonium nitrate propellants, particularly of the cross-linked double-base (XLDB) type. Thus, it has been found that the addition of relatively small amounts as 0.5 percent to about 8.0 percent, but preferably from about 1.0 to about 3.0 percent bismuth trioxide has resulted in a more controllable and usable burn rate for propellant compositions of the XLDB class.
With respect to the present invention, XLDB propellants are of a relatively more hazardous class (mass-detonable) and the bismuth trioxide is added for a different purpose. That reference does not disclose the use of Bi.sub.2 O.sub.3 in propellents of the class of the present invention (non-mass-detonable) nor the possibility of using Bi.sub.2 O.sub.3 to replace significant amounts of other oxidizing materials in such compositions, including the fact that a gain in total thrust might be achieved by doing so.
The use of certain polyether-type polymer binders has also been disclosed in relation to solid composite propellant compositions of the class of the present invention by Goleniewski et al in U.S. Pat. No. 5,349,596. Those binders include non-crystalline polyethers used to improve safety in combination with inert plasticizers, i.e., plasticizers which do not have a positive heat of explosion (HEX).
Another patent to Goleniewski et al (U.S. Pat. No. 5,783,769) reveals solid composite propellant compositions that employ non-crystalline polyether binders in combination with energetic plasticizers (positive HEX).
There remains a need and quest in the art to produce more efficient propellant performance in solid propellant compositions for rocket motors. Accordingly, it is a primary object of the present invention to provide solid composite propellant compositions having enhanced performance which include an oxidizer fraction having a significant amount of bismuth trioxide (Bi.sub.2 O.sub.3).
Other objects and advantages will become apparent to those skilled in the art upon familiarization with the specification and claims herein.